Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$114.25	13.605%	$129.7937	$129.79	$129.80	$129.80
Purchase #2	$199.40	11.648%	$222.6261	$222.63	$222.65	$222.60
Purchase #3	$183.54	4.845%	$192.4325	$192.43	$192.45	$192.40
Purchase #4	$157.60	8.390%	$170.8226	$170.82	$170.80	$170.80
Purchase #5	$246.58	10.114%	$271.5191	$271.52	$271.50	$271.50
Purchase #6	$59.85	12.433%	$67.2912	$67.29	$67.30	$67.30
Purchase #7	$35.33	9.272%	$38.6058	$38.61	$38.60	$38.60
7 purchase totals =	$996.55		$1,093.0910	$1,093.09	$1,093.10	$1,093.00